1. Field of the Invention
The present invention relates an efficient method of grafting compounds which contain an amino group, such as polyoxyalkylene amines, to polyamides, such as polyaspartic acid, polyglutamic acid, and copolymers of aspartic and glutamic acids, with pendant carboxylic acid groups. The present method also relates to the graft polymers produced by such a process. The present invention further relates to compositions which contain such graft polymers and methods of using such graft polymers.
2. Discussion of the Background
Polyaspartate is economically produced by the thermal polymerization of aspartic acid or precursors of aspartic acid such as maleic acid and ammonia. The initial product is polysuccinimide (synonyms: polyanhydroaspartic acid, polyaspartimide), which is composed of residues of succinimide, the cyclic imide of aspartic acid. A review of patents and other literature dating to 1850 on the synthesis of polyaspartate and polysuccinimide is provided in U.S. Pat. No. 5,594,077 (Groth et al), which is incorporated herein by reference. The production of polyaspartic acid by the thermal polymerization of aspartic acid and hydrolysis of the thus-obtained polysuccinimide is shown schematically below: 
Synthesis of potentially useful derivatives of polysuccinimide and polyaspartate also has a long history. A common approach has been the nucleophilic addition of primary amines such as ethanolamine to form an amide linkage upon opening of the imide ring of a succinimide residue, producing a polysuccinimide with pendant groups (see: U.S. Pat. No. 3,846,380 (Fujimoto et al)). Because polysuccinimide is insoluble in water, the reactions are normally accomplished in organic solvents such as dimethyl formamide or N-methyl pyrrolidone. The derivatized polysuccinimide can be converted to a derivatized polyaspartate by mild alkaline hydrolysis of the remaining imide rings.
Thermal copolymerization of aspartic acid and other monomers also has frequently been reported beginning with U.S. Pat. No. 3.052,655 (Fox et al) and extending to U.S. Pat. No. 5,658,464 (Hann et al). U.S. Pat. No. 5,357,004 (Wood et al); U.S. Pat. No. 5,442,038 (Wood et al); U.S. Pat. No. 5,502,117 (Wood et al); U.S. Pat. No. 5,510,426 (Wood et al); U.S. Pat. No. 5,510,427 (Wood et al); U.S. Pat. No. 5,519,110 (Wood et al); U.S. Pat. No. 5,521,279 (Wood et al); U.S. Pat. No. 5,371,179 (Paik et al); U.S. Pat. No. 5,371,177 (Paik et al); U.S. Pat. No. 5,410,017 (Bortnick et al); and U.S. Pat. No. 5,478,919 (Koskan et al) disclose copolymers produced by synthetic routes that included monoamines of polyoxyalkylenes. Applications such as detergent additives, dispersants, corrosion inhibitors, antiscalants, additives to fertilizers, additives to oral health care products and cosmetics, and others were disclosed.
Japanese Patent Application 7-172888 (Nagatomo et al) discloses derivatives of polysuccinimide and polyaspartate prepared by nucleophilic addition of monoamines such as ethanolamine and taurine to polysuccinimide in dimethyl formamide or water. Cement admixtures containing polyaspartic acid and these derivatives are disclosed, and some effects on the flow of Portland cement are disclosed.
Derivatives of polyaspartate have also been formed by thermal addition of coreactants to a preformed polyaspartate. U.S. Pat. No. 5,247,068 (Donachy et al); U.S. Pat. No. 5,260,272 (Donachy et al); and U.S. Pat. No. 5,284,936 (Donachy et al) disclose that the use of a preformed polyaspartate as a reactant lead to improvements as compared to the copolymerization of monomeric reactants.
U.S. Pat. No. 5,552,516 (Ross et al); U.S. Pat. No. 5,612,384 (Ross et al); U.S. Pat. No. 5,461,085 (Nagatomo et al); U.S. Pat. No. 5,525,682 (Nagatomo et al); U.S. Pat. No. 5,525,703 (Kalota) and WO 95/35337 (Ross et al); WO 96/08523 (Ross et al); and EP 0 658 586 A1 (Nagatomo et al) each disclose aqueous reactions of diamines with polysuccinimide to effect nucleophilic addition at elevated pH with the object of producing water-soluble, high MW, crosslinked polyaspartates upon alkaline treatment of the crosslinked polysuccinimides. Alternatively, if the degree of crosslinking is sufficient, water-absorbent, insoluble materials were produced.
A problem with this approach is that the OHxe2x88x92 groups in water at elevated pH compete with the NH2 groups of the diamines to donate electrons to imide rings of the polymer, thus ring-opening the polysuccinimide residues by hydrolysis. Another problem is that the polysuccinimide is hydrophobic and water-insoluble such that much of the polysuccinimide is not readily available for reactions in the aqueous phase. Consequently, elevated amounts of diamines are required and the reactions are inefficient and incomplete, leaving partially reacted as well as unincorporated diamines.
U.S. Pat. No. 5,639,832 (Kroner et al) discloses the aqueous reaction of monoamino compounds such as amino ethyl sulfonate (taurine), other amino acids, and monoamino poly(propylene-ethylene)glycol with polysuccinimide at elevated pH. Graft efficiency no higher than 60% was reported. The materials produced by the reactions, which include the entire mixture of reactants and products at the end of the reactions, are disclosed as being useful as detergent additives, dispersants, and antiscalants.
In addition to polyaspartates, other polyanionic polymers such as polyacrylates have been derivatized with polyoxyalkylene side chains via thermal reaction of monofunctional groups of the derivatizing compound and the carboxyl groups of the polymer (see: U.S. Pat. No. 5,393,343 (Darwin et al); U.S. Pat. No. 5,614,017 (Shawl); and U.S. Pat. No. 5,670,578 (Shawl)). The derivatized polyacrylates are disclosed as being useful for improving the rheological properties of cement, acting as water-reducing and plasticizing additives.
Dispersants are used to improve the flow characteristics of cement slurries by breaking up cement agglomerates and freeing the water, thus giving the slurries of lower viscosity and allowing desirable flow conditions to be obtained at lower pump pressures. V. S. Ramachandran, Concrete Admixtures Handbook: Properties, Science, and Technology, Second Edition, Noyes Publications, 1995, which is incorporated herein by reference. Superplasticizers such as sulfonated melamine formaldehyde condensate (SMF) and sulfonated naphthalene formaldehyde condensate (BNS) are commonly used as dispersants. However, these compounds require more than the desired amount of material to achieve a desired level of concrete workability or water reduction. In addition, these materials do not achieve the full range of water reducing capability for the various types of concrete admixtures (e.g., Type A and Type F as defined in ASTM C494 etc.).
It is important that dispersants are used in concrete situations where strength and durability are involved, as dispersants are a necessary component in high strength and high durability concretes. Due to the use of low water amounts in the high performance concretes, sometimes high dispersant amounts are necessary to achieve workable concretes. High BNS levels can lead to undesirable retardation of set and may not provide the required workability retention over time.
It is desirable to provide a material that is several times more efficient as a cement or concrete dispersant than the traditional materials like BNS and SMF. Improving efficiency reduces the amount of material required to achieve a desired level of concrete workability or water reduction. With respect to BNS and SMF, it is also desirable to improve slump retention while maintaining normal setting characteristics. Providing a dispersant with full range (Type A and F) water reducing capability is also a desirable characteristic.
Thus, there remains a need for a method of preparing polyamides, such as polyaspartatic acid and polyglutamic acid, which contain pendant carboxylic acid groups grafted with amino compounds, such as methoxylated polyoxyalkylene amines, in high yield without the use and expense of excess coreactants or organic solvents. Such a method would involve no waste disposal and produce no harmful byproducts. There also remains a need for improved surfactants and dispersants for use as additives to cementitious materials.
Accordingly, it is one object of the present invention to provide a novel method of grafting compounds which contain amino groups to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups.
It is another object of the present invention to provide a method of grafting compounds which contain amino groups to polyamides , such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups which method achieves a high graft efficiency and therefore does not require the use of excess grafting agent.
It is another object of the present invention to provide a method of grafting compounds which contain amino groups to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups which method does not require the use of organic solvents.
It is another object of the present invention to provide a method of grafting compounds which contain amino groups to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups which method affords graft polymers with a high graft density.
It is another object of the present invention to provide novel graft polymers in which compounds which contain amino groups are grafted to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups.
It is another object of the present invention to provide novel graft polymers, having a high graft density, in which compounds which contain amino groups are grafted to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups.
It is another object of the present invention to provide novel compositions which contain such graft polymers in which compounds which contain amino groups are grafted to polyamides, such as polyaspartic acid and polyglutamic acid, which contain pendant carboxylic acid groups.
It is another object of the present invention to provide novel methods of improving the flow properties of cement.
These and other objects of the present invention, which will become apparent during the following detailed description, have been achieved by the inventors"" discovery that heating an intimate mixture of a polyamide, such as polyaspartic acid and polyglutamic acid, which contains pendant carboxylic acid groups with a compound which contains an amino group affords a graft polymer in which the compound which contains an amino group is grafted to the polyamides which contain pendant carboxylic acid. The inventors have also discovered that the graft polymers so produced are useful as additives to cementitious materials.